The present invention relates to a dielectric motor which is driven by means of electric fields and which has rotors which are surrounded by several electrodes.
Engines of this type are suited for miniaturization and can be combined with microelectronic elements (system integration). They can be employed as drive means for miniaturized machines or pumps, as circuit elements or for position determination. For example, step by step operation can serve to clear or block optical channels for the transmission of data. The position can be determined by having the rotor only turn when the corresponding component takes up a specific position. Another field of application is use in micro-surgical instruments.
Descriptions of non-stop running motors driven by constant electric fields including their modus operandi and calculation of their rotational behavior can be found in Journals in the art (e.g. Secker, P. E.; Scialom, I. N.; A Simple Liquid Immersed Dielectric Motor, Journal of Applied Physics, 39, 1968, p. 2957 to 2961). The starting direction of rotation is not fixed in these motors so that additional auxiliary devices are required for starting.
The Japanese published patent JP-A-1 107 667 describes a motor in which two cylindrical rotors are excited to rotate about separate axes of rotation under the electrostatic influence of electrodes which are attached to the interior wall of a hollow cylinder.
Miniaturized dielectric motors of different design are described in GEO 10, 1988, page 188 and in the U.S. Pat. No. 4,740,410. In these motors rotating electric fields are utilized so that start devices are obviated. In the European patent EP-A-O 233 947 a dielectric motor is described, whose rotor is provided with radially disposed sector like dielectrics. In these described motors, excitation is based on an electrostatic effect. Alternating fields are also always arranged under quasi stationary conditions. For this reason the rotors of these motors always turn in the direction of the rotating field, consequently they are synchronous motors. The field of application of motors of this type is restricted by this characteristic.
With the publication "Dielektrische Motoren" in ELEKTRIE 43, 1989, 2, pages 45 to 50, a dielectric motor which has several fixed electrodes disposed around a central region has become state of the art. In the central region are two rotors made of dielectric material and disposed in a rotatable manner, which are driven by means of electric fields. Excitation occurs via a mutual field of excitation. The flexibility of the rotation conditions of this motor is limited due to the fact that the motion of the rotors is synchronous.
An object of the present invention is to provide a dielectric motor which has an influenceable rotational characteristic and which has a multiplicity of simple to adjust rotational conditions.
This and other objects are provided in a generic dielectric motor by rotors being made of different dielectric materials and having spatially separate axes of rotation.
Due to the disposition of the rotors in the same central electrode-bordered region, the rotors are driven via the same excitation field. The number and arrangement of the rotors in the central region result in various rotational conditions which can be utilized for suitable applications.
The rotors are made of different dielectric materials. By this means the various rotors are driven diversely by the same excitation field. The rotors may turn in the same or in opposite direction and have the same or different angular velocity.
In an alternative embodiment of the invented motor, at least one rotor is not axially symmetrical in design. This can be achieved by this rotor having regions made of different dielectric materials which are arranged in an axially asymmetrical manner relative to the axis of rotation. The rotor may, however, also have a geometric shape which is asymmetrical relative to the axis of rotation. Due to the axially asymmetrical design, the individual rotor already has various conditions of rotation. In combination with the additional rotors this further increases the number of total conditions of rotation.
According further to the present invention, at least one rotor has a fixed position in the central region of the motor. The position of the spatially not fixed rotors depends on the excitation field, the position of the other rotors, the surrounding medium and the position of the dielectric motor. Thus, conclusions can be drawn about, e.g., the position of the motor, by determining the rotational conditions. In this embodiment the rotors can be partially, constantly or never in mechanical contact with one another or with the electrodes.
The possible conditions can also be influenced according to another embodiment of the invention by conductive regions being built into the rotors or according to another embodiment of the invention by electrically polarizable elements being attached in the central region of the motor. These measures influence the rotational characteristic of the individual rotors. Thus the various rotors can be operated continuously, discontinuously or step by step at one and the same time.
An improvement of the present invention is provided in another embodiment of the invention. The rotors are designed as toothed drums. If two adjacent toothed drums are set in motion in opposite directions, the teeth of the drums accelerate a surrounding medium in a preferred direction. This improvement of the present invention is therefore suited as a pump for fluid or gaseous media. In this event it is advantageous according to another embodiment of the invention if at least one of the rotors is deformable. This embodiment prevents the closely adjacent rotors from being destroyed by a solid element in the pump medium.
According further to the present invention, the driving electric fields are strongly asynchronous to the rotational motion of the rotors. The rotor and field direction of rotation may be the same or opposite. The electric field may turn with up to 10.sup.7 greater velocity than the rotors.
The effects achieved with the present invention are intensified according to another embodiment of the invention by the electric field turning with an amplitude which changes per rotation. The rotation of the electric fields can be discontinuous according to another embodiment of the invention, by way of illustration, by applying phase-shifted square-wave voltages to the electrodes. In this manner, discontinuous rotation of one or all the rotors can be forced.
The invented motor can be especially strongly miniaturized. According further to the present invention, the motor is fabricated out of one substrate with the aid of micromechanical production methods. In this way, the motors can be produced with an expansion of less than 100 .mu.m.
Used as a substrate is, by way of illustration, silicon, possibly provided with thin layers of insulation such as SiO.sub.2, Si.sub.3 N.sub.4, or glass. The electrodes are structured by employing photolithographic methods and galvanically molded, e.g. with gold. In this manner the electrode pattern can be defined with micrometer precision. By employing deep etch lithography, electrode heights of several 100 micrometers can be obtained.
The rotors are made of dielectric materials also using micromechanical processes. Rotors of heights in the micrometer range are fabricated out of the applied layers. Higher rotors can be made out of photographic lacquer using deep etch lithography.
Exact grooves and channels for fixing the rotor or conducting the surrounding solution of the motor in or out are etched into the substrate with isotropic or anisotropic and selective etching processes. A rotor axis connected to the substrate can also be fabricated with the same process. An encapsulation of the system can be achieved by means of a second wafer bonded onto the substrate wafer. The use of silicon as the substrate material makes it possible to integrate electric circuits for triggering and controlling the motor with the mechanical elements on the same substrate.
The advantages of the present invention are that many rotational conditions can be presented which can be utilized for various purposes. The motor can serve as a switch element or a variable drive. Microdosing devices, pumps and valves can be designed which can be utilized in technology, pharmacology, chemistry and biotechnology. As a result of the high degree of miniaturization, the starting time of the motor lies in the microsecond range.